South Africa's Nuclear Model

by Tom Ferreira

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Developments Marking Progress

An exciting new development is PBMR (Pty) Ltd's intention to submit a proposal for the US$ 1.1-billion hydrogen production project at the Idaho National Environmental and Energy Laboratory in the USA. The hydrogen initiative calls for a plant that can generate both electricity and high temperature process heat. Initial conceptual layouts show that, with minor modifications, the current PBMR power plant can meet this requirement.

Participation in the hydrogen project offers clear benefits that can act as a catalyst for the early commercialization of the PBMR technology in the USA. This would lead to the reactor becoming the preferred route as far as HTR technology is concerned.

Uranium fuel spheres

The PBMR concept is based on the philosophy that new reactors should be small. The reactor consists of a vertical steel pressure vessel lined with graphite bricks. It uses silicon carbide coated particles of enriched uranium oxide encased in graphite to form a fuel sphere or pebble, each containing about 15,000 uranium dioxide particles. Helium is used as the coolant and energy transfer medium.

The project achieved a major engineering milestone with the successful starting up of a test rig of the PBMR power conversion system. The test rig represents the first closed cycle, multi-shaft gas turbine in the world. The model was designed and built by the Faculty of Engineering at Potchefstroom University near Johannesburg, with technical input from the PBMR project team.

The South African Nuclear Energy Corporation, which is under contract from PBMR (Pty) Ltd to develop the fuel manufacturing capability, is in the meantime making good progress. Its focus is on developing the exacting production techniques required for the manufacture of complete fuel spheres.

Demonstrating Safety

The design's fundamental concept is aimed at achieving a plant having no physical process that could cause a radiation hazard beyond the site boundary. In addition, the peak temperature reached in the core during the transient is not only below the demonstrated fuel degradation point, but also far below the temperature at which the physical structure is affected. This will preclude any prospect of a core melt accident.

The safe design was proven during a public and filmed plant safety test at the German AVR power plant, on which the PBMR reactor core concept is based. The Germans stopped the flow of coolant through the reactor core and left the control rods withdrawn just as if the plant was in normal power generation mode.

It was demonstrated that the nuclear reactor core shut itself within a few minutes. It was subsequently proven that there was no deterioration over and above the normal design failure fraction of the nuclear fuel. This proved that a reactor core meltdown was not credible and that an inherently safe nuclear reactor design had been achieved.

"We're trying to change the nuclear culture," says Phumzile Tshelane, General Manager Corporate Services of PBMR (Pty) Ltd. "If the PBMR demonstration module proves to be technically and commercially viable, it could dramatically boost the prospects of nuclear energy on a global scale, fulfilling at last the dream of a non-polluting power source that is safe, competitive and perhaps even popular."

Joining Forces for Innovation

South Africa already operates two conventional nuclear power plants at Koeberg, which together supply about 6% of the country's electricity, including most of nearby Cape Town's needs. Electricity demands are expected to keep rising in years ahead. About 60% of South Africans today have access to electricity, compared to 30% a decade ago. Nuclear and renewable sources of energy helped fuel the growth, though coal remains the dominant power source, generating 90% of all electricity.

Pebble bed reactors are not new to the nuclear world, though technological innovations now are helping to bring them to market. If built, South Africa's PBMR would be the largest commercial example of the technology.

Both Germany and China have developed PBMRs, and research and development is intensifying in the United States, China and other countries. Recently, researchers at the Massachusetts Institute of Technology (MIT) in the US and Tsinghua University in Beijing, China formed a partnership to collaborate on PBMR development under an international agreement between the US Department of Energy and the China Atomic Energy Authority.

For the past six years, MIT and Tsinghua research teams have been working independently on studies of the reactor. Their joint work now sets up ways for the research teams to exchange technologies and ideas.

"The agreement provides an incredible opportunity for bringing the world together on this promising technology," says Professor Andrew Kadak of the Department of Nuclear Engineering, who leads the MIT research and was instrumental in the three-year effort to get the agreement signed. He is now contacting other pebble-bed researchers in the United States, Europe, South Africa and elsewhere to develop mutual topics of interest. The aim is to form an international effort that will go far beyond the MIT/Tsinghua collaboration and build on worldwide interest in the technology.

One focus of interest is a "plug-and-play" approach to building components of pebble bed reactors. If competitive, researchers say such small, modular plants will be attractive not only to the US market but also to China and other rapidly developing countries that have widely dispersed populations.

Tom Ferreira is Communication Manager of PBMR (Ltd.) in South Africa (https://www.pbmr.com). E-mail: [email protected]

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